Restore Referer-Policy and wrap up MbedTLS changes

redbean will now set Referer-Policy to no-referrer-when-downgrade on
text/html responses by default. There's better explanations on the bits
of security redbean is offering. In short, it's 128+ for modern clients
and 112+ for legacy. If the -B flag is used then it's 192+ for modern
and 150+ for non-EC.

third_party/mbedtls/everest.c

@@ -242,7 +242,6 @@ static void HaclEcAddAndDoubleFmonty(uint64_t xz2[2][5], uint64_t xz3[2][5],
 
 /**
  * Computes elliptic curve 25519.
- * @note it has 126 bits of security
  */
 void curve25519(uint8_t mypublic[32], const uint8_t secret[32],
                 const uint8_t basepoint[32]) {